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Powered subwoofer has hum - JBL SCS145.5 System

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JP gave you the correct answer. If the hum is there with nothing connected, the hum is ac (60 cycles) not being properly filtered out in the sub woofer amp's power supply. Check the filtering capacitors that are in the supply - often they go bad - look for leaking or bulging units. If all look fine you will have to remove from circuit and use a cap tester to resolve issue.

Posted on Mar 29, 2015

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Hum is a ground problem. Here is what u can do... plug all components into a single outlet. Use a new multi outlet power strip. Run all your plugs to it even if it means you run across the room to that power strip with a extension cord. If one power strip is not enough add another to it. The important thing is that your ground goes into one ground. Grounds get dirty an the flow may go in all directions...by putting the into one plug you eliminate that issue. Vast improvement for your humm....n pop, that maybe a power supply issue..

Posted on Mar 25, 2015

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  • Master
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First of all confirm if the hum is an internal or external problem.
Disconnect the RCA sub woofer input from the back of the unit and turn it on. If there is no hum it could be the interconnecting cable or the output from the receiver. But in the stand alone mode if the sub woofer hums when powered on you have internal problem and will have to be looked into by a professional.
Many a time the earth or the shield of the interconnecting cable is the culprit, because the sub sits on the floor and you might shift it for cleaning the floor and the cable can stretch and snap internally.

Posted on Apr 01, 2011

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Posted on Jan 02, 2017

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4 Answers

Klh powered subwoofer model ASW10-120B... when you plug in to power... it makes a loud buzzing/humming noise


I would check the caps on the power supply. They are rather large electrolytic capacitors that will look like they burst and/or leaking. When these die, the caps ground and the sub will make a loud buzzing sound. If you are handy with a soldering iron you can replace them yourself. Replace them with the same voltage or a little bigger and same with the size.

If the cap. says 16v 4700pF on it, for example, a 20v 5300pF or a 16v 6200mF cap. will work for this application.

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Jan 05, 2016 | Audio Players & Recorders

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Why does my HTS-20 powered subwoofer make a low hum when plugged in, even turned off and not connected to the receiver and a louder hum when the subwoofer power is turned on?


I suspect the amplifier is damaged. This is not an easy repair to do unless you are well versed in audio electronics. I would recommend a repair shop to look at the subwoofer amplifier.

Jun 03, 2015 | Infinity HTS-20 System

1 Answer

After a power outage I have a loud hum.


Hi, The Ground Rules Of all the annoyances that can afflict any audio/video home theater or even a simple stereo installation, the notorious "ground loop" may well be the most difficult and persistent one to track down and eliminate. A "ground loop" is caused by the difference in electrical potential at different grounding points in an audio/video system. (All the grounds in an A/V system should ideally be at "0" potential.) A ground loop typically adds a loud low-frequency hum or buzz as soon as you plug in any of various audio or video components, including subwoofers, cable-TV outboard boxes, satellite-TV feeds, TV displays, amplifiers, A/V receivers or turntables. The buzz/hum is a byproduct of the multiple power supply cables and a ground voltage differential within your system and its network of interconnecting cables.

Here are some methods to help you get rid of ground loops. Try these first and don't waste money on a power "conditioner" which, in most cases, won't help. (There is no need to "condition" the AC power for your system. Your receiver or amplifier already has a power supply with its own filters and transformers. No further filtering is normally required.)

If you get your system up and running and hear an audible buzz or hum, the first culprit to look at is either the powered subwoofer or your cable-TV or satellite-box feed at the entry point to your system.

First, the subwoofer: unplug the coaxial cable that connects to your powered subwoofer to see if the ground-loop hum disappears. If it does, it's likely coming in through your cable/satellite TV feed.

Reconnect your subwoofer's coaxial cable from the subwoofer input to your receiver's subwoofer output and disconnect the cable-TV feed (or satellite feed) from your outboard set-top cable box or satellite tuner. Be sure and disconnect the cable before any splitters. Now see if the hum/buzz from your subwoofer stops.

If that eliminates the hum, you can install one of these inexpensive in-line ground isolators from Parts Express or Bass Home. Note that these transformer-based ground isolators will work fine with analog cable-TV feeds, but depending on their design they may interfere with or block reception of HDTV signals via a digital cable or satellite dish feed.

Install the ground isolator between the cable-TV feed and the input of your outboard cable-TV box or satellite tuner (or the TV display's antenna or cable input if you have a set with a built-in TV tuner or a cable-card ready set). In many cases, the ground isolator will "break" the loop and remove the annoying hum or buzz by isolating the TV-cable ground.

If a hum remains with the TV cable completely disconnected from your system, or you don't want to risk degrading reception of HD signals from a cable or satellite system, then you may have to add a ground isolator like this Radio Shack Model 270-054 between the line-level coaxial subwoofer cable from your A/V receiver and the line-level input jack on your powered subwoofer.

In all cases, if your subwoofer has a ground-lift screw like some of Axiom's subwoofers, try first removing the screw (or replacing it) to see if it increases or eliminates the hum. It may or may not make a difference.

If you do not have easy access to the aforementioned ground isolators, here are a few more tips:

Try plugging the subwoofer into a different AC outlet in the room, one that isn't supplying power to your components (A/V receiver, TV, cable box, etc.). That might fix it.

Try reversing the AC plug for your A/V receiver or the powered subwoofer. If it's a 3-wire plug or a polarized plug, which has one prong wider than the other, you won't be able to reverse the plug. For safety, do not use a "cheater plug" to bypass the 3-wire plug.

With the power OFF, reverse the AC plugs one by one of any other components that have a standard 2-prong AC plug that isn't polarized. Each time you reverse a plug, turn on the system with the attached component and your subwoofer and see if the hum disappears. In some cases, reversing one or more plugs will eliminate the hum.

If you have a turntable, try connecting a separate ground wire to a chassis screw on your preamp or receiver and see if the hum disappears. If you already have a turntable ground wire, try removing it from the preamp. One or the other may eliminate the hum.

Finally, here is another solution that worked well for a member of our message boards who decided to discard his ground-loop isolator on his subwoofer: "I took off the ground-loop isolator I'd been using and connected a plain 14-gauge wire to chassis screws on the sub and the receiver then powered everything on. Although hum was still there, it was far lower than before. Next I unscrewed the ground-loop screw on the back of the sub and that took care of the hum completely."

Almost certainly sounds like an earth loop to me, but can be caused by a poorly made transformer or phase shifts on the mains supply. Visit some power conditioner web-sites like Isotek or Isol-8 (or google "earth loop") where there's plenty of advice on how to reduce/eliminate earth loops and other causes of mains-induced hum (transformer problems etc).

Hum on the speakers usually indicates that there is a DC voltage on the speaker line. DC voltage on the output lines would be caused by a shorted output transistor.


Have a nice day...

Feb 16, 2011 | Cambridge Soundworks BassCube 12 Speaker

1 Answer

Sunfire MK II Subwoofer hum. I have a Sunfire MK II subwoofer that hums when it is plugged in (it even hums when no signal is connected). I've tried multiple outlets on different circuits, but hum...


you have a ground loop issue you could purchase a ground loop isolator, jensen makes them for about 40 bucks.I have discovered that if you have cable tv, unplug the incoming cable in your cable box and see if hum disappears.

Nov 25, 2010 | Sunfire True Sub MK II Subwoofer

1 Answer

How to get rid of the hum


Check your cabling to make sure you dont have a ground fault. if you still have humming, buy a "groundless" adapter for your power plug (takes the ground away) and plug it back into the power outlet and I bet your humming will be gone

May 10, 2010 | Sunfire True Sub MK II Subwoofer

1 Answer

Loud hHum from Subwoofer


Sounds like the hum might be mains hum caused by the failure of the power supply capacitor(s) in the sub. It/they will be the largest on the pc board. You will find all the details (needed to replace it) on them. If you find more than one replace both.

Dec 10, 2009 | Audio Players & Recorders

1 Answer

Humming sound when on/off


humming sound when on is usual if the volume is turned up.
humming sound the same when on or off could be transformer plates fluxing.
if loud recommend replacement of power supply.
if ok then recommend unplugging the device after use.

Nov 13, 2009 | Velodyne DPS-10 Subwoofer

5 Answers

Subwoofer making load humming noise


The reason for the hum in the Altec Lansing VS4121 speaker system is the stray field of the power supply transformer. This stray field is strong enough to affect the amplifier. All other reasons given by numerous reports on the web do not apply. If you are handy and have got the time you may mitigate the problem by physically moving the amp away from the power supply or turning it 90 degrees. I managed to lift up the amp in my subwoofer by about 50 mm, which was difficult to achieve and did not cure the problem perfectly. I don't see any other way to solve this problem except you feed DC in from the outside and do not use the internal power supply. That would be really odd indeed

Gerhard Weber.

Jan 29, 2009 | Altec Lansing VS4121 Speaker

1 Answer

Subwoofer hum


Hi,

Based on your description, the internal power supply of the subwoofer amplifier would be suspect. Often it would be a blistered or leaking filter capacitor. It is a relatively easy/inexpensive repair.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information. Good luck and kind regards. Thank you for using FixYa.

Nov 09, 2008 | Jensen JHT525 System

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